Combined feedforward-feedback noise reduction schemes for open-fitting hearing aids

Over the past years, the usage of open-fitting hearing aids has been steadily increasing, due to the fact that they largely alleviate occlusion-related problems. However, existing noise reduction (NR) schemes that only use the external microphones on the hearing aid do not take into account the ambient noise leaking through the open fitting, such that this leakage may even counteract the noise reduction performed by the hearing aid. Integrating active noise control (ANC) motivated algorithms into existing NR schemes by exploiting a built-in internal (error) microphone in the ear canal, enables to partially compensate for this noise leakage. This paper presents a combined feedforward-feedback ANC (FF-FB ANC) scheme for open-fitting hearing aids. For different gains of the hearing aid, it is shown that the SNR improvement of the combined FF-FB ANC scheme outperforms a feedforward ANC and a classic Multichannel Wiener Filter noise reduction scheme without ANC. In addition, the frequency-dependent SNR improvement is analysed for different microphone positions, i.e., at the entrance of the ear canal and at the eardrum.